The objective of the proposed research is the determination of the three dimensional structure and function of two sugar-binding proteins from E.Coli, nar L-arabinose-and D-galactose-binding proteins, by X-ray crystallographic technique Sugar-binding proteins are components of specific transport systems in membrane of living cells. These transport systems are responsible for the relative constant of the internal environment of the cell. L-arabinose-and D-galactose-binding proteins function in the transport of L-arabinose and D-galactose, respectively. Once the structure of the sugar-binding proteins is known, crystallographic method can be further utilized to obtain detailed knowledge of the stereochemistry of sugar binding. Structural changes attendant to binding of sugars, as has been indicated for D-galactose- binding protein, can be elucidated in detail by X-ray analysis. In view of the presently held concept that binding proteins are involved in the transport process and would therefore be expected to function and interact in a membrane environment, a detailed comparative study of the mode of their folding and the stability of their unique three-dimensional structure may provide some understanding of the nature of protein- membrane interaction. The occurrence of similarities in structure among binding proteins may reflect those portions of the molecule that participate in membrane interactions. The determination of the structure of sugar-binding proteins will contribute to some understanding of the molecular basis of transport systems. These systems allow cells to extract fuels and other essential nutrients from the environment, maintain constant and optimal internal concentrations of inorganic electrolytes, serve as barriers to waste products being excreted, and participate in the regulation and maintenance of metabolic steady state.